Conventionally, suction pipettes for sucking and measuring a fixed volume of a relatively small amount of liquid or the like have been used in various fields. Particularly, push-button type suction pipettes used with a suction tip attached to the tip are frequently used in biochemical experiments and the like. Although a suction pipette is used for sucking a fixed volume of liquid, it is also used for the purpose of moving subjects from a certain place to another as a preliminary usage.
Examples of subjects include not only liquids, but also powders, particles, cells and the like contained in liquids (hereinafter, these are referred to as a collection of subjects in some cases). These subjects such as powders have various shapes and sizes (hereinafter, these are referred to as shapes in some cases). In many cases, impurities having a small diameter are removed in advance from subjects to eliminate shape deviations of the subjects and prevent the clogging of a device used due to fine impurities. Particularly, in the fields of bio-related technology and medicine, since a large amount of impurities such as organelles and disrupted cell membranes are included in the case of using disrupted liquid of cells or the like, such impurities having a small diameter are selected and removed in an initial stage of a test.
An old method using a sieve has been known as a selection method. However, in the case of selection using a sieve or the like, there are problems of deteriorating operation efficiency and consuming rare subjects and causing contamination before and after the selection.
In view of such problems, suction tips and suction pipettes provided with a subject selection mechanism have been proposed. Japanese Unexamined Patent Publication No. 2009-34013 discloses a suction pipette in which a cup-shaped storage portion including an opening with a predetermined opening area is provided around a nozzle for sucking subjects. This suction pipette sucks and selects subjects having a diameter smaller than the opening area. Japanese Unexamined Patent Publication No. 2006-115781 discloses a filter unit which can be used for a suction pipette and in which a film filter is mountable. The filter unit of Japanese Unexamined Patent Publication No. 2006-115781 is used by being mounted in a pipette tip of a suction pipette and filters cells and the like from subjects by the thin film filter mounted inside.